The “INESA Lighting Handbook” published by the Illuminating Engineering Society of North America, is incorporated by reference here in its entirety. As discussed in chapter seven of that handbook, a “luminaire” is a device for producing, controlling, and distributing light. It is typically a complete lighting unit consisting of one or more lamps, sockets for positioning and protecting the lamps and for connecting the lamps to a supply of electric power, optical devices for distributing the light, and mechanical components for supporting or attaching the luminaire. Luminaires are also sometimes referred to as “light fixtures.”
Luminaires are usually classified by their application, such as residential, commercial, or industrial. However, a particular luminaire can often be used in more than one application, depending upon its performance characteristics. For example, recessed downlights are used in both commercial and residential applications where they are typically mounted behind a ceiling wall with an opening to produce illuminance on the floor or workplace below.
Various support systems have been employed to carry recessed luminaires in buildings and other structures. For example, recessed fixtures are often suspended between joists, or other parallel support structures, on a pair of “hangar bars” or “bar hangars” extending between the joists. Similar hangar bar arrangements are used to suspend recessed downlights between the rails in a suspended, tile ceiling.
These conventional hangar bars are often formed in one-piece with a fixed length so as to provide adequate structural rigidity at a relatively low cost. For example, U.S. Pat. No. 5,505,419 to Gabrius (assigned at issuance to Juno Lighting) is incorporated by reference here in its entirety and discloses a one-piece bar hangar having a stiffening rib that extends along substantially the entire length of the bar hangar. In order to change its length, the bar must be broken along a single score line. Since the length of the hangar bar cannot be variably adjusted, its use is often limited to joists, or other supports, having a standard and consistent spacing.
Hangar bars have also been devised with an adjustable two-piece configuration. For example, U.S. Pat. No. 5,029,794 to Wolfe (assigned at issuance to Prescolite) is incorporated by reference here and discloses a pair of bar hangar elements that are nested in a slidable relationship relative to each other. Each bar hangar element is identical in construction with an elongated slot and two retaining projections.
U.S. Pat. No. 4,723,747 to Karp et al. (assigned at issuance to Capri Lighting) is also incorporated by reference here and discloses a two-piece bar hangar with an elongated slot as well as a longitudinally extended “dome,” or projection, to facilitate nesting. One of the hangar bar elements has an arrow-shaped retaining projection while the other hangar bar element has a foot-like retaining projection that is received within the slot.
As with single-piece hangar bars, two-piece hangar bars may be trimmed for use with smaller joist spacings. However, these hangar bar assemblies must generally be disassembled prior to altering their length. Furthermore, while such two-piece arrangements permit installation between supports or joists of various spacings, they generally suffer from a lack of stability that fails to provide adequate support for the suspended luminaire, especially when the hangar is installed in its fully-extended, or nearly fully-extended, position.
In this regard, U.S. Pat. No. 6,076,788 to Akiyama (assigned at issuance to Cooper Industries) is incorporated by reference here and discloses a hangar bar assembly with a first bar hangar having a plurality of longitudinal slots, each separated by a reinforcing formation. A second hangar bar member having a plurality of spaced retaining projections is interfitted with the first hangar bar member. At least one of the retaining projections engages at least one of the slots in order to couple the hangar bar members as they are extended longitudinally.
Each of the Akiyama hangar bar members may also include a score line for allowing a portion of the hangar bar member to be removed in order to reduce the overall length of the hangar bar assembly. Although such hangar bar assemblies generally provide adequate support in their fully-extended position, the hangar bar members must be separated in order to change their length by breaking each member along its score line. Furthermore, such conventional hangar bars can generally be used with only one particular type of ceiling configuration.